Top Botany Stories of 2003

A giant fungus, Armillaria ostoyae, has put a stranglehold on a forest in the Pacific Northwest by weaving tangled filaments called rhizomorphs through the soil and around the roots of trees.

Greg Filip

Foresters Find World’s Largest Organism, a Humongous Fungus

Every autumn, tree-killing honey mushrooms burst from the ground in Oregon’s Blue Mountains and leave patches of dying firs in their wake. U.S. Forest Service researchers recently gathered spore samples from various locations for lab analysis and

Courtesy of Greg Filip

A giant fungus, Armillaria ostoyae, has put a stranglehold on a forest in the Pacific Northwest by weaving tangled filaments called rhizomorphs through the soil and around the roots of trees.

made a startling discovery. The golden mushrooms are actually offshoots of a single monstrous subterranean fungus—the size of 1,800 football fields—that could be the largest living organism on Earth. Genetic test results published in April suggested that the supersize fungus, from the species Armillaria ostoyae, was spawned by the sexual recombination of two separate mushrooms as long ago as 6000 B.C. “It spread out underground through shoestringlike filaments known as rhizomorphs, forming a giant patchwork,” says plant pathologist Catherine Parks, the head of the research team. “It challenges the customary notion of what we think of as an ‘individual.’”

The discovery “opens up exciting possibilities about how forests are affected by what goes on underground,” says Cindy Prescott, coeditor of the Canadian Journal of Forest Research, in which the surprising study appeared. Previously, researchers wrongly assumed that the suppression of natural forest fires had contributed to the spread of the fungus. Now it appears that the most effective means of containing the ever-encroaching organism may be to plant fungus-resistant trees, such as western larch, Ponderosa pine, and western white pine. Armillaria ostoyae is an important part of the food chain in the forest, so the goal is to control the fungus, not eliminate it. Besides, says Parks, with a little garlic and butter, the golden spores are quite delicious.